1. Field of the Invention
The invention relates to a novel one-step process for preparation of phenol by hydroxylation of benzene with hydrogen peroxide catalyzed by molecular sieves doped with copper ions. With proper solvent, a phenol yield of 15-35%, selectivity close to 100% and phenol/Cu TON around 100 could be achieved at a temperature lower than 80.degree. C.
2. Description of the Prior Art
Phenol is an important compound for industry and pharmaceuticals. It can be used as a starting material as well as an intermediate for manufacture of many chemicals, such as dyes, bactericides and herbicides. Therefore, its demand has always been extremely great; its annual world production had been reached to 4.9.times.10.sup.6 tons in 1996[K. Weissermel and H. J. Arpe, "Industrial Organic Chemistry", 3.sup.rd ed., VCH Publishers, Inc., New York, N.Y., U.S.A. 1997, p. 347]. Although a direct oxidation process of benzene to phenol would be the most economical route, until now only the indirect manufacturing processes have been operated, that is, benzene was reacted at first into an intermediate which was then reacted into phenol. The reason resided in that the oxidation capability of phenol is higher than that of benzene and the selectivity of one-step oxidation of benzene into phenol is generally not high. In United State and Japan, the most popular process operated presently for phenol production is the cumene process [K. Weissermel and H. J. Arpe, supra, p. 347], which includes the catalytic alkylation of benzene to cumene and consequent oxidation of cumene to phenol and acetone. Acetone is generated in stoichiometric amount as the side product. The complication of this multi-step process as well as the cost of product separation leave the direct oxidation of benzene to phenol in a single step to be of great challenging to synthetic chemists.
In Europe, a two-step process was used predominantly [K. Weissermel and H. J. Arpe, supra, p. 347], wherein toluene as the starting material was subjected to a catalytic oxidation to form benzoic acid which was then decomposed catalytically into phenol and carbon dioxide. These processes were not, of course, as economic as the one-step oxidation of benzene into phenol.
Many approaches for one-step direct oxidation of benzene into phenol have been reported, yet little success has been achieved due to low phenol yield, expensive oxidants, and high operating cost. For example, a process using ZSM-5 zeolite as catalyst and N.sub.2 O as oxidant has been well examined as an one-step reaction for oxidizing benzene into phenol (see, for example, V. I. Sobolve, A. S. Kharitonov, Y. A. Paukshtis and G. I. Panov, J. Mol. Catal., 1993, 84, 117; R. Burch and C. Howitt, Appl. Catal., 1992, 86, 139; J. S. Yoo, A. R. Sohail, S. S. Grimmer and J. Z. Shyu, Appl. Catal., A: General 1994, 117, 1). Its greatest disadvantage resided in that it should be operated at an elevated temperature of higher than 200.degree. C. and N.sub.2 O is an expensive oxidant which resulted in an undue high cost.
Another process whose reaction mechanism often been discussed is one using divalent iron as the catalyst and hydrogen peroxide as oxidant (Fenton's reaction) (J. R. Lindsay-Smith and R. O. C. Norman, J. Chem. Soc., 1969, 2897). However in view of the catalytic efficiency, its phenol yield was extremely low, the turnover number (TON, or phenol yield per active site) was around 1, and that rendered it evidently of little developing potential.
Furthermore, liquid phase reactions using Ti- or V-containing zeolites as catalysts and hydrogen peroxide as oxidant have been reported (J. S. Reddy, S. Sivasanker and P. Ratnasamy, J. Mol. Catal., 1992, 71, 373; A. V. Ramaswany, S. Sivasanker and P. Ratnasamy, Micro. Mater., 1994, 2, 451), wherein some deep oxidation side products such as p-benzoquinone and hydroquinone were produced and the phenol selectivity was not high. The same reaction using tetra-nuclear platinum complex as a catalyst has been proposed (A. V. Ramaswany, S. Sivasanker and P. Ratnasamy, Micro. Mater., 1994, 2 , 451), and the difficulty laid in the preparation of such a catalyst. Still another process using ammonium salt of mono-vanadium(V)-substituted hetero-polyamines as the catalyst has been tried (K. Sakai and K. Matsumoto, J. Mol. Catal, 1991, 67, 7), but a low phenol yield was obtained. Recently, an one-step process for oxidizing benzene into phenol was reported, wherein a mesoporous molecular sieve, MCM-41, either exchanged with copper ion or loaded with copper oxide was used as the catalyst, 10 atm of oxygen as oxidant, ascorbic acid as reducing agent and acetic acid as solvent (K. Nomiya, K. Yagishita, Y. Nemoto and T. Kamataki, J. Mol. Catal. A, 1997, 126, 43). Although it claimed to have a very high phenol selectivty, the use of ascorbic acid and acetic acid as well as the formation of di-ketones as side products could increase the difficulty in product separation. Furthermore, its phenol yield did not exceed 1.5%, and its phenol/Cu TON was not higher than 15. This report revealed also that hydrogen peroxide generated during the reaction was the true oxidant.
References
1. K. Weissermel and H.-J. Arpe, "Industrial Organic Chemistry", 3.sup.rd ed., VCH Publishers, Inc., New York, N.Y., U.S.A. 1997, p. 347. PA0 2. V. I. Sobolve, A. S. Kharitonov, Y. A. Paukshtis and G. I. Panov, J.Mol.Catal., 1993, 84, 117 PA0 3. R. Burch and C. Howitt, Appl.Catal., 1992, 86, 139 PA0 4. J. S. Yoo, A. R. Sohail, S. S. Grimmer and J. Z. Shyu, Appl. Catal., A:general 1994, 117, 1 PA0 5. J. R. Lindsay-Smith and R. O. C. Norman, J. Chem. Soc., 1969, 2897 PA0 6. J. S. Reddy, S. Sivasanker and P. Ratnasamy., J.Mol.Catal., 1992, 71 ,373 PA0 7. A. V. Ramaswany, S. Sivasanker and P. Ratnasamy., Micro. Mater., 1994, 2, 451 PA0 8. K. Sakai and K. Matsumoto, J.Mol.Catal, 1991, 67, 7 PA0 9. K. Nomiya, K. Yagishita, Y. Nemoto and T. Kamataki, J. Mol. Catal A, 1997, 126, 43 PA0 10. J. Okamura, S. Nishiyama, S. Tsuruya and M. Masai, J. Mol. Catal. A., 1998, 135, 133.
In addition, many related patents are described as follows:
(1) In relation to the process via acid-catalyzed decomposition of cumene hydroperoxide into phenol and acetone, a number of solid acid catalysts has been used instead of sulfuric acid which is used in the current industrial process for the acid-catalyzed decomposition. See, for example, U.S. Pat. Nos. 4,870,217 (1989), 4,898,987 (1990), 4,898,995 (1990), 4,209,465 (1980), 4,246,203 (1981), 4,267,379, 4,267,380 (1981), and 4,482,757 (1984); and JP Patent No. 54157531 (1979). PA1 (2) Monsanto Company has developed in recent years a process for one-step oxidizing benzene into phenol by using N.sub.2 O as oxidant and iron-containing zeolite as the catalyst at a reaction temperature of 225-600.degree. C. Such a process was proposed mainly by the research group of Gennadii I. Panov in Russia. The related patents were as follows: U.S. Pat. Nos. 5,110,995 (1992), 5,672,777 (1997), 5,756,861 (1998), 4,559,314 (1985), 4,982,013, 5,001,280, 5,055,623, 5,077,026 (1991), 5,098,687, 5,110,995 (1992), and 5,367,099 (1994); JP Patent No. 06009464 (1994); RU Patent No. 2010790 (1994); GB Patent No. 2116974 (1983); and WO Patent Nos. 9500066, and 9500065 (1995). PA1 (3) Since the catalytic ability of Ti-silicalite for the hydroxylation of aromatics was discovered, there have been many patents disclosed in applications of Ti- or V-containing molecular sieves to such reactions. See, for example, U.S. Pat. Nos. 5,783,167 (1998), 5,569,791 (1996), 5,246,689, 5,198,203, 5,196,633 (1993), 5,174,888, 5,102,643, 5,098,684 (1992), and 5,064,629 (1991); and WO Patent Nos. 9429022 (1994), 9302013 (1993), and 9118833 (1991). PA1 (4) As a part of the multiple-step reaction using toluene as the starting material in the European process for production of phenol, the decarboxylative hydrolysis of chlorobenzoate salt was disclosed in U.S. Pat. No. 3,912,784 (1975), and the oxidative decarboxylation of arylcarboxylic acids or their salts, esters, and anhydrides, was disclosed in U.S. Pat. Nos. 4,405,823, 1983; and 5,210,331, 1993. PA1 (5) Still other processes are as the following:
(i) steam oxidation of cyclic or open-chain alkane to phenols, catalyzed by ZnO/TiO.sub.2, ZnO/V.sub.2 O.sub.5, ZnO/TiO.sub.2 /La.sub.2 O.sub.3 and the like (U.S. Pat. No. 4,061,685, 1977). PA2 (ii) hydrolysis of iodobenzene in a liquid phase, catalyzed by cuprous salts such as Cu.sub.2 O, CuI, CuCl and the like (U.S. Pat. No. 4,684,749, 1987).
Among these mentioned processes, only those of (2) and (3) were one-step processes for oxidation of benzene into phenol. The Monsanto process using iron-containing ZSM zeolites as catalysts and N.sub.2 O as oxidant has a greatest disadvantage as it must be carried, out at an elevated temperature of 225-600.degree. C. and its production cost is greatly determined by the price of N.sub.2 O oxidant at different production area thereof. On the other hand, the process involving liquid phase reactions using Ti- or V-containing zeolites as catalysts and hydrogen peroxide as oxidant may generate some deep oxidation side products such as hydroquinone and benzoquinone. This explains why Ti- or V-containing zeolites have been used as catalysts in industrial processes for manufacture of hydroquinone and catechol through hydroxylation of phenol but not for producing phenol.